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                [BeiJing2010组队]次小生成树 Tree                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：512MB</p>			</div>
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                                <h3>题目描述</h3><p><p>小 C 最近学了很多最小生成树的算法，Prim 算法、Kurskal 算法、消圈算法等等。 正当小 C 洋洋得意之时，小 P 又来泼小 C 冷水了。小 P 说，让小 C 求出一个无向图的次小生成树，而且这个次小生成树还得是严格次小的，也就是说： 如果最小生成树选择的边集是 EM，严格次小生成树选择的边集是 ES，那么需要满足：(value(e) 表示边 e的权值) <img alt="" border="0" src="../file/1977_0.jpg" /> 这下小 C 蒙了，他找到了你，希望你帮他解决这个问题。</p></p><hr/><h3>输入格式</h3><p><p>第一行包含两个整数N 和M，表示无向图的点数与边数。 接下来 M行，每行 3个数x y z 表示，点 x 和点y之间有一条边，边的权值为z。</p></p><hr/><h3>输出格式</h3><p><p>包含一行，仅一个数，表示严格次小生成树的边权和。(数据保证必定存在严格次小生成树)</p></p><hr/><h3>样例输入</h3><pre>5 6 
1 2 1 
1 3 2 
2 4 3 
3 5 4 
3 4 3 
4 5 6 </pre><hr/><h3>样例输出</h3><pre>11</pre><hr/><h3>提示</h3><p><p>数据中无向图无自环； 50% 的数据N&le;2 000 M&le;3 000； 80% 的数据N&le;50 000 M&le;100 000； 100% 的数据N&le;100 000 M&le;300 000 ，边权值非负且不超过 10^9 。</p></p><hr/><h3>题目来源</h3><p>没有写明来源</p>
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